Such, Gentlemen, was the man, whofe memory you wish to preferve in the Records of your Society. I knew him better than any perfon living, and I loved him more than I fhall attempt to exprefs. I have not, however, dealt in unmixed eulogy, which fometimes may amuse the living, but which can never characterife the dead. It belonged to him I have attempted to commemorate, to be as jealous of undeferved praise, as of undeferved cenfure; and I have endeavoured to delineate his character, in fuch a manner, as his magnanimous fpirit would have approved. I have not, knowingly, extenuated his faults; and you will not believe, I have fet down ought in malice. What would it avail me to deviate from the truth? The voice of cenfure cannot pierce the grave, nor flattery footh the ear of death.

J. C.

LIVERPOOL, September 30, 1784.

A TRANSLATION

A TRANSLATION of Dr. BELL'S THESIS, de PHY

SIOLOGIA PLANTARUM.

By JAMES CURRIE,

M.D.* Read March 30, 1785.

D

IFFERENT parts of nature have drawn the attention of different philofophers. While fome men of the greatest genius have employed themselves in the ftudy of their own fpecies; others have been diligently engaged in investigating the properties of the inferior claffes of animals. Nor are thofe to be placed in the lowest class of philofophers, whose time and attention are engroffed by that immenfe portion of nature, the Vegetable Kingdom; though, it is to be regretted that, in general, their obfervations have been directed more to the external form of plants, than to their internal ftructure.

The knowledge of the internal ftructure of vegetables unfolds their economy, and, from a discovery of this, not only botany, but agriculture, might receive great improvement. But

The original was published at Edinburgh, June 1777, and dedicated to doctors CULLEN and HOPE, in Janguage, which expreffes a high admiration of their talents and virtue, and a deep fenfe of gratitude for the favours received from them, by the AUTHOR.

this fubject is as difficult, as it is important, and, as yet, it is not precifely understood, even by the most curious obfervers. I am led to engage in it more by the pleafing nature of the study, than the hope of furpaffing those who have gone before me; and I purpose, in the following Effay, to confine myself to a few remarks on the ftructure, life, and functions, of vegetables.

It is proper to premife, that if the anatomy of plants be not demonstrated throughout, with all the clearness that could be wifhed, this arifes from their containing parts of fuch a degree of minuteness, that they elude the human fight. The nature of these must therefore frequently be inferred from analogy only, which is often fallacious. But many things have been ascertained on this fubject, and with these I shall begin.

On making a tranfverfe fection of a tree, it appears to confift of three diftinct parts-the bark-the wood-and the medulla, or pith.

1. The bark confifts of two parts--the cuticle, and the true bark. The cuticle of plants affords an external covering to all their parts. It confifts of numerous layers, eafily feparable from each other, and of which the fibres are circular.*

The

* Dr. Hill, by the ufe of magnifying glaffes, first discovered the cuticle to be an organized body, containing longitudinal veffels, and veficles, &c. He however thought, the cuticle was formed merely by the hardening of the fuperficies of the true bark, when exposed to the external

air.

The true bark may be confidered as a congeries of cellular fubftance, in which are placed two kinds of organs, the vasa propria, or the veffels peculiar to the plants, and the longitudinal fibres. Of the use of thefe, nothing can be faid at prefent.

2. On removing the bark, the wood appears. Its fubftance is denser than the bark, and its ftructure more difficult to be demonstrated. But it has been difcovered likewife to contain vafa propria, and longitudinal fibres, and, befides thefe, large veffels with fpiral coats, which run from one end of the tree to the other, and are denominated vafa aëria. Between the wood and the pith lies a green coloured fubftance, first accurately described by Dr. John Hill, and by him affirmed to contain all the parts of the plant in embryo: he gave it the name of Corona.

3. In the centre of the tree refides the pith, which, in young plants, is very abundant. As they approach to maturity it grows drier, and appears in a smaller quantity; and, in very aged trees, it is entirely obliterated. Its fubítance is cellular, and, according to the author juft men

air. In this he was mistaken, because it is found in the heart of fruits, covering the feed, and because Du Hamel, and Dr. Hope found, that, when the cuticle is removed, and the acceffion of the air prevented by wax-cloth, this covering is nevertheless in a little while restored.

tioned,

tioned, it is of a fimilar ftructure in all plants. These are the folid parts of vegetables.

But there are likewife fluids, or juices in vegetables; and thefe are of two kinds. The one is of the fame nature in all the variety of vegetables: the other varies according to the different plants in which it exists. The former, which is called the fuccus communis, when collected early in the spring, from an incision made in the birch or vine, differs little from common water.* The latter, which is named the fuccus proprius, poffeffes various properties in various plants, and gives to each its fenfible qualities. These two juices never mingle with each other in the tree, and the latter is found in the vasa propria only.

It is not yet afcertained, whether the juices of plants are tranfmitted through veffels, or cellular fubftance. Each fide of the question has had its advocates, who have fupported their respective opinions with probable arguments but it is to be regretted, that, on fo

It has, however, been alledged to contain a faccharine matter in fome trees, as in the maple, &c. It has likewife been fuppofed to contain an acid. But, in various experiments which Dr. Bell made on it, he found nothing in it of either kind; and therefore, where fuch appearances have taken place, he fuppofed them to arife from an adventitious mixture of the fap, and the fuccus proprius.

J. C.

interesting